The invention relates to a semiconductor diode laser comprising a semiconductor body with a substrate of a first conductivity type and a semiconductor layer structure situated thereon and having an active layer arranged between two cladding layers and a pn junction by which electromagnetic radiation can be generated in a strip-shaped active region of the active layer given a sufficient current strength in the forward bias direction, an end face of the strip-shaped active region being curved so as to form a lens of a given strength. The invention also relates to a method of manufacturing such diode lasers.
Such diode lasers are used inter alia as components in read and/or write heads of information processing equipment such as laser printers, bar code readers, and read and/or write devices for optical registration carriers such as CD (Audio) and CDROM (Data) discs, and as transmitters in systems for optical glass fibre communication. In the latter systems, the semiconductor diode laser may also be constructed as an amplifier. Accordingly, the term laser in the present Application is explicitly understood also to cover a laser amplifier.
Such a diode laser is known from JP(A) 3-119.782 published in Patent Abstracts of Japan, vol. 15, no. 323 (E-1101) [4851] 16th Aug. 1991. The strength (P) of the lens is determined by the equation P=.DELTA.n/R in which .DELTA.n is the difference in refractive index between the active region 3 and the surrounding medium, i.e. air, and R is the radius of curvature of the curved end face. The said difference in refractive index is approximately 2.5, namely approximately 3.5-1. A lens strength which is usual in practice corresponds to a radius of curvature R which lies between approximately 10 and approximately 300 .mu.m, often between 20 and 50 .mu.m.
A disadvantage of the known device is that an increase in the starting current is often observed with the use of lasers having an active region with a curved end face as compared with similar lasers having a plane end face. Such an increase is obviously undesirable.